Method and System to Combine Multiple Encoded Videos

ABSTRACT

Methods and systems described herein provide for combining multiple data streams representing respective videos into an output data stream. An example implementation may involve receiving a first data stream that represent a first video and a second data stream that represent a second video. The first data stream and the second data stream may include a first sequence of frames that includes first intra-coded frames and a second sequence of frames that includes second intra-coded frames, respectively. The example implementation may further involve combining the received first data stream and the received second data stream to obtain an output data stream of encoded output frames such that an encoded output frame includes a respective frame of the first sequence and a respective frame of the second sequence and that first intra-coded frames are combined with respective second intra-coded frames in respective encoded output frames within the output stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/267,486, filed on May 1, 2014, entitled “Method and System to CombineMultiple Encoded Videos For Decoding Via A Video Decoder,” which isincorporated herein by reference in its entirety.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Media, such as video and audio, is often compressed to reduce thequantity of data needed to represent the media (commonly known as thebit rate). By reducing the bit rate, a smaller amount of data storagemay be needed to store the video and less bandwidth may be needed totransmit the video over a network. Numerous video codecs(coder/decoders) exist as hardware and/or software components thatenable compression or decompression of digital video. To decodecompressed video, many types of computing devices have hardware and/orsoftware decoding units.

Decoding video can be a CPU-intensive task, especially for higherresolutions like 1080p. Therefore, while video decoders may beimplemented as software modules that execute on general purposeprocessors, in many circumstances, specialized hardware decoders may bemore efficient and/or more capable, especially with regards to decodinghigher-resolution video. Some low-power devices, such mobile computingdevices, may be equipped with general purpose processors that may havedifficulty decoding high-resolution video in real-time and/or within anacceptable power envelope. To assist in decoding such videos, somemobile computing devices, such as smartphones and tablets, may beequipped with one or more hardware video decoders configured to decodecompressed video.

BRIEF SUMMARY

In one example, a method is provided that includes receiving, by aprocessor, a first data stream that represents encoded frames of a firstvideo and receiving a second data stream that represents encoded framesof a second video. For each frame of the received first data stream, themethod further includes defining in a header of the frame that the frameis a first slice of a respective output frame. And, for each frame ofthe received second data stream, the method includes defining in aheader of the frame that the frame is a second slice of the respectiveoutput frame and that the second slice is stacked vertically underneaththe first slice in the respective output frame. The method then includesgenerating an output data stream that is configured to represent theencoded frames of the first video as respective first slices of encodedoutput frames and to represent the encoded frames of the second video asrespective second slices of the encoded output frames such that arespective output frame is divided into a respective first slice and arespective second slice. The method also includes sending the generatedoutput data stream to a decoder.

In another example, a computer readable storage memory is provided thathas stored therein instructions, that when executed by a processor,cause the processor to perform functions. The functions comprisereceiving a first data stream that represents encoded frames of a firstvideo and receiving one or more additional data streams that eachrepresent encoded frames of a respective video. For each encoded frameof the received first data stream, the functions also comprise combininga respective frame of each of the one or more additional data streamswith the encoded first frame such that each encoded first frame includesa respective frame of the first video and a respective frame of each ofthe one or more additional data streams. The functions further comprisedecoding, by a particular decoder, each combined frame of the first datastream into an output surface format that represents the frames of thefirst video and the frames of each of the videos of the one or moreadditional data streams. The functions also comprise providing forconcurrent display the decoded frames of the first video and the decodedframes of each of the videos of the one or more additional data streams.

In still another example, a device is provided that comprises one ormore processors and data storage configured to store instructions, thatwhen executed by the one or more processors, cause the device to performfunctions. The functions comprise receiving a first data stream thatrepresents encoded frames of a first video, where each encoded frame ofthe first video is divided into a respective first macroblock array, andreceiving a second data stream that represents encoded frames of asecond video, where each encoded frame of the second video is dividedinto a respective second macroblock array. The functions also comprisecombining the received first data stream and the received second datastream into an output data stream that is configured to representencoded output frames. Each encoded output frame includes the secondmacroblock array of a respective encoded frame of the second videovertically concatenated to the first macroblock array of a respectiveencoded frame of the first video. The functions further comprisedecoding the output data stream into an output surface format thatincludes, in respective non-overlapping regions, decoded frames of thefirst video and decoded frames of the second video and providing thedecoded frames of the first video and the decoded frames of the secondvideo for display.

In yet another example, a system is provided that includes a means forreceiving a first data stream that represents encoded frames of a firstvideo and a means for receiving one or more additional data streams thateach represent encoded frames of a respective video. For each encodedframe of the received first data stream, the system further includes ameans for combining a respective frame of each of the one or moreadditional data streams with the encoded frame of the first video suchthat each encoded frame includes a respective frame of the first videoand a respective frame of each of the one or more additional datastreams. The system further includes a means for decoding, by aparticular decoder, each combined frame of the first data stream into anoutput surface format that represents the frames of the first video andthe frames of each of the videos of the one or more additional datastreams. The system further includes a means for providing for displaythe decoded frames of the first video and the decoded frames of each ofthe videos of the one or more additional data streams.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an example computing device by which an examplemethod may be implemented.

FIG. 2 illustrates example components of an example computing device.

FIG. 3 is a flowchart illustrating an example method for combiningmultiple encoded video streams for concurrent decoding.

FIG. 4A illustrates example components of an example video data stream.

FIG. 4B illustrates example sub-components or sub-portions of theexample video data stream.

FIG. 5A illustrates example frames of video data streams.

FIG. 5B illustrates example slices of the video data streams.

FIG. 5C illustrates an example frame of a combined video data stream.

FIG. 6 illustrates example sequenced data streams and a combined streamrepresenting the example sequenced data streams.

FIG. 7 illustrates an example frame of another combined video datastream.

FIG. 8 illustrates an example frame of yet another combined video datastream.

FIG. 9 illustrates example slices and an example output frame thatcombines the example slices.

FIG. 10 represents example ordered data streams having different framerates and a combined stream representing the example ordered datastreams.

DETAILED DESCRIPTION

The following detailed description describes various features andfunctions of the disclosed systems and methods with reference to theaccompanying figures. In the figures, similar symbols identify similarcomponents, unless context dictates otherwise. The illustrative systemand method embodiments described herein are not meant to be limiting. Itmay be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

A given computing device may have a video decoder that assists thecomputing device in decoding encoded videos. In some cases, the videodecoder may be implemented within the computing device as specializedhardware configured to execute specific code algorithms which functionto decode video. The specialized hardware may support decoding a certainnumber of video streams concurrently. For instance, the specializedhardware may include a total of two hardware decoder units, each ofwhich may support decoding one video at a time.

At the same time, some applications may provide for displaying morevideos concurrently than the specialized hardware can decodeconcurrently. For example, a video chat application that supports groupchat with multiple computing devices concurrently may provide forconcurrent display a video stream from each computing device. As anotherexample, a news feed application may provide for display of a previewvideo next to each news item in a news feed of multiple news items. Whenan application provides for the concurrent display of more video streamsthan a given computing device supports in hardware, the computing devicemay decode one or more of the video streams using a software decoder.However, decoding in software on a general purpose processor is nottypically as efficient as decoding on a hardware decoder. In some cases,the general purpose processor on which the software decoder is executingmay not be fast enough to decode the one or more video streams inreal-time. Also, in some cases, decoding in software may significantlyincrease the processor utilization, which may negatively affect the userexperience in various ways, such as by causing the UI to feel sluggishor unresponsive. In some cases, decoding a video in software may alsouse relatively more battery charge than used by decoding the video usingspecialized hardware. As an alternative to decoding with a softwaredecoder, manufacturers may include additional decoding units in theircomputing devices. However, this solution may increase the cost andpower consumption of the computing devices.

Within examples, methods and systems are provided for decoding, via asingle video decoder, multiple compressed video sources for concurrentdisplay. For example, a processor may receive two or more data streamsthat each represent an encoded video. The processor may then combine thetwo or more data streams into an output data stream that representsframes having content from each of the two or more data streams. Theprocessor may then provide the output data stream as input to a videodecoder, which may provide decoded frames that include content from eachof the two or more video streams. The processor may then divide theoutputted frames into their component videos.

It should be understood that arrangements described herein are forpurposes of example only. As such, those skilled in the art willappreciate that other arrangements and other elements (e.g. machines,interfaces, functions, orders, and groupings of functions, etc.) can beused instead, and some elements may be omitted altogether according tothe desired results. Further, many of the elements that are describedare functional entities that may be implemented as discrete ordistributed components or in conjunction with other components, in anysuitable combination and location, or other structural elementsdescribed as independent structures may be combined.

Referring now to the figures, FIG. 1 illustrates an example computingdevice 100 by which an example method may be implemented. Computingdevice 100 may include applications 102 a and 102 b and an operatingsystem 104 being executed by hardware 106. Although the examplecomputing device 100 is a smartphone, aspects of this disclosure areapplicable to other computing devices such as PCs, laptops, tabletcomputers, etc.

Each of the applications 102 a and 102 b may include instructions thatwhen executed cause the computing device 100 to perform specific tasksor functions. Applications 102 a and 102 b may be native applications(i.e., installed by a manufacturer of the computing device 100 and/or amanufacturer of the operating system 104) or may be a third-partyapplication installed by a user of the computing device 100 afterpurchasing the computing device. A non-exhaustive list of exampleapplications includes: a media player application that accepts mediafiles as inputs and generates corresponding video and/or audio to theoutput device(s); a video gallery application; a video communicationapplication (e.g. a video chat or video call application); an e-readerapplication which accepts electronic documents (books, magazines, etc.)as input and presents the content of the document via the outputdevice(s); a feed reader that accepts feeds delivered over the Internet(e.g., RSS feeds and/or feeds from social network sites) as input andpresents the feeds via the output device(s); a map application thatdisplays a map via the output device(s); a note-taking application, abookmarking application, and a word processing, spreadsheet, and/orpresentation application that accepts specifically formatted files asinputs and presents them via the output devices for viewing and/orediting.

The operating system 104 may interact with and manage hardware 106 toprovide services for the applications 102 a and 102 b. For example, anapplication 102 a may request that the operating system 104 direct anintegrated camera of hardware 106 to capture a visual image and that thehardware 106 store the image to memory.

The hardware 106 may include, for example, a central processing unit(CPU), a graphics processor (GPU), memory, an input/output (I/O)interface, user input device(s), and output device(s). Components ofhardware 106 may be controlled by instructions contained in applications102 a and 102 b and operating system 104.

The central processing unit (CPU) may be operable to effectuate theoperation of the computing device 100 by executing instructions storedin memory or disk storage. Such instructions may include the operatingsystem 104 and the applications 102 a and 102 b. The CPU may, forexample, comprise a single or multi-core processor, an applicationspecific integrated circuit (ASIC), field programmable gate array(FPGA), and/or any other suitable circuitry.

The graphics processor may be operable to generate a video stream foroutput to the screen based on instructions and/or data received from theCPU. That is, data structures corresponding to images to be displayed onthe screen may be stored to and read from the memory or disk storage bythe CPU. The CPU may convey such data structures to the graphicsprocessor via a standardized application programming interface (API)such as, for example, Standard Widget Toolkit (SWT), the DirectX VideoAcceleration API, the Video Decode Acceleration Framework API, or othersuitable API.

The memory may include program memory and run-time memory. The memorymay, for example, comprise non-volatile memory, volatile memory, readonly memory (ROM), random access memory (RAM), flash memory, magneticstorage, and/or any other suitable memory. Program memory may storeinstructions executable by the CPU to effectuate operation of theoperating system 104 and the applications 102 a and 102 b. Runtimememory may store data generated or used during execution of theoperating system 104 or applications 102 a and 102 b.

The input/output (I/O) interface may be operable to receive signals fromthe input device(s), and provide corresponding signals to the CPU and/orthe graphics processor.

The input device(s) may include, for example, a mouse, a touchpad, amotion sensor, a trackball, a voice recognition device, a keyboard, orany other suitable input device which enables a user to interact withthe computing device 100.

The output devices may include, for example, a screen and speakers. Thescreen may be, for example, a liquid crystal display (LCD) screen, anOLED screen, an e-ink screen, and/or any other suitable device forpresenting a graphical user interface.

FIG. 2 illustrates example components of an example computing device,such as the example computing device 100 in FIG. 1, among otherexamples. In some examples, some components illustrated in FIG. 2 may bedistributed across multiple computing devices. However, for the sake ofexample, the components are shown and described as part of one exampledevice 200. The device 200 may be or include a mobile device, desktopcomputer, laptop computer, email/messaging device, tablet computer, orsimilar device that may be configured to perform the functions describedherein.

In some implementations, the device 200 may include a device platform(not shown), which may be configured as a multi-layered Linux platform.The device platform may include different applications and anapplication framework, as well as various kernels, libraries, andruntime entities. In other examples, other formats or systems mayoperate the device 200 as well.

The device 200 may include an interface 202, a wireless communicationcomponent 204, a cellular radio communication component 206, sensor(s)208, data storage 210, and a processor 212. Components illustrated inFIG. 2 may be linked together by a communication link 216. The device200 may also include hardware to enable communication within the device200 and between the device 200 and another computing device (not shown),such as a server entity. The hardware may include transmitters,receivers, and antennas, for example.

The interface 202 may be configured to allow the device 200 tocommunicate with another computing device (not shown), such as a server.Thus, the interface 202 may be configured to receive input data from oneor more computing devices, and may also be configured to send outputdata to the one or more computing devices. In some examples, theinterface 202 may also maintain and manage records of data received andsent by the device 200. In other examples, records of data may bemaintained and managed by other components of the device 200. Theinterface 202 may also include a receiver and transmitter to receive andsend data. In other examples, the interface 202 may also include auser-interface, such as a keyboard, microphone, touchscreen, etc., toreceive inputs as well.

The wireless communication component 204 may be a communicationinterface that is configured to facilitate wireless data communicationfor the device 200 according to one or more wireless communicationstandards. For example, the wireless communication component 204 mayinclude a Wi-Fi communication component that is configured to facilitatewireless data communication according to one or more IEEE 802.11standards. As another example, the wireless communication component 204may include a Bluetooth communication component that is configured tofacilitate wireless data communication according to one or moreBluetooth standards. Other examples are also possible.

The cellular radio component 206 may be a communication interface thatis configured to facilitate wireless data communication according to oneor one cellular radio standards. For example, the cellular radiocomponent 206 may include a cellular radio that is configured tofacilitate wireless data communication according to one or more cellularstandards, such as the Global System for Mobile Communications (GSM),Code Division Multiple Access, Long-Term Evolution (LTE), WorldwideInteroperability for Microwave Access (WiMax), among others.

The sensor 210 may include one or more sensors, or may represent one ormore sensors included within the client device 200. Example sensorsinclude an accelerometer, gyroscope, pedometer, light sensors,microphone, camera, or other location and/or context-aware sensors.

The data storage 212 may store program logic 218 that can be accessedand executed by the processor 212. The data storage 210 may also storedata 220 that may include data received by any of the wirelesscommunication component 204, the cellular radio communication component206, the GPS 208, and any of sensors 210. For instance, the data storage212 may store one or more data streams that represent video.

The processor 212 may be a general purpose processor that may accessprogram logic 218 that can be retrieved and executed by the processor212. The processor may include one or more decoder(s) 222 that may beconfigured to decode encoded video. A non-exhaustive list of examplevideo codecs that may be processed by the one or more decoder(s) 222include MPEG (e.g. H.264/MPEG-4 AVC and H.265/MPEG-H HEVC), WindowsMedia Video (WMV), On2 (e.g. VP8 and VP9), Sorenson, Dirac, Cinepak, andRealVideo.

The device 200 is illustrated to include a graphics processing unit(GPU) 214. The GPU 214 may be configured to control other aspects of thedevice 200 including displays or outputs of the device 200. The GPU 214may include one or more decoder(s) 224 that may be configured to decodevideo that has been compressed using one or more of the above-referencedvideo codecs, among other examples.

The communication link 216 is illustrated as a wired connection;however, wireless connections may also be used. For example, thecommunication link 216 may be a wired serial bus such as a universalserial bus or a parallel bus, or a wireless connection using, e.g.,short-range wireless radio technology, communication protocols describedin IEEE 802.11 (including any IEEE 802.11 revisions), or Cellulartechnology, among other possibilities.

Example methods described herein may be performed individually bycomponents of the device 200, or in combination by one or all of thecomponents of the device 200. In one instance, portions of the device200 may process data and provide an output internally in the device 200to the processor 212, for example. In other instances, portions of thedevice 200 may process data and provide outputs externally to othercomputing devices.

FIG. 3 is a block diagram of an example method 300 to provide fordecoding multiple compressed video sources via a video decoder forsimultaneous display, in accordance with at least some embodimentsdescribed herein. Method 300 shown in FIG. 3 presents an embodiment of amethod that, for example, could be used with a computing device, such ascomputing device 100 in FIG. 1 or device 200 in FIG. 2, among otherexamples. Method 300 may include one or more operations, functions, oractions as illustrated by one or more blocks of 302-308. Although theblocks are illustrated in a sequential order, these blocks may in someinstances be performed in parallel, and/or in a different order thanthose described herein. Also, the various blocks may be combined intofewer blocks, divided into additional blocks, and/or removed based onthe desired implementation.

In addition, for the method 300 and other processes and methodsdisclosed herein, the flowchart shows functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer readable medium, forexample, such as a storage device including a disk or hard drive. Thecomputer readable medium may include a non-transitory computer readablemedium, for example, such as computer-readable media that stores datafor short periods of time like register memory, processor cache andRandom Access Memory (RAM). The computer readable medium may alsoinclude non-transitory media, such as secondary or persistent long termstorage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media may also be any other volatile or non-volatile storagesystems. The computer readable medium may be considered a computerreadable storage medium, a tangible storage device, or other article ofmanufacture, for example. The program code (or data for the code) mayalso be stored or provided on other media including communication media,such as a wireless communication media, for example.

In addition, for the method 300 and other processes and methodsdisclosed herein, each block in FIG. 3 may represent circuitry that iswired to perform the specific logical functions in the process.

Functions of the method 300 may be fully performed by a processor of acomputing device, or may be distributed across multiple components of acomputing device. In some examples, the functions of method 300 may bedistributed across multiple computing devices and/or a server.

At block 302, the method 300 involves receiving a first data stream thatrepresents encoded frames of a first video and receiving a second datastream that represents encoded frames of a second video. While thefunctions of receiving the first data stream and receiving the seconddata stream are discussed herein as one function, they may beimplemented as separate functions which may be performed in differentways. Also, while a first data stream and a second data stream aredescribed by way of example, the present method may involve receiving aplurality of data streams, such as a third data stream and a fourth datastream.

For instance, processor 212 of device 200 in FIG. 2 may receive thefirst data stream and the second data stream. In some examples,processor 212 may receive the first data stream and the second datastream from another computing device via interface 202 and communicationlink 216, for example. In other examples, processor 212 may receive thefirst data stream and the second data stream from data storage 210 viacommunication link 216. Computing device 200 may temporarily store (i.e.buffer) the first data stream and the second data stream in data storage210 when the first data stream and the second data stream are receivedvia interface 202. Alternatively, computing device 200 may store thefirst data stream and the second data stream as video files in datastorage 210. Other examples are possible as well.

A video may include a sequence of images (also known as frames). Asnoted above, the first data stream may represent encoded frames of afirst video and the second data stream may represent encoded frames of asecond video. For instance, any suitable computing device may haveencoded one or more frames of the first video into the first data streamusing a video codec. Further, any suitable computing device may haveencoded one or more frames of the second video into the second datastream. Any suitable video codec may be used to encode the frames,including without limitation, MPEG-developed codecs (e.g. H.264/MPEG-4AVC and H.265/MPEG-H HEVC), Windows Media Video (WMV), On2 codecs (e.g.VP8 and VP9), Sorenson, Dirac, Cinepak, or RealVideo. Although theprocessor may receive first video and second videos as encoded datastreams, encoding the first video and/or the second video are notnecessary aspects of the invention.

Depending on the video codec used to encode the first video, the firstdata stream and the second data stream may be arranged into differentformats. As noted above, in some circumstances, the videos may beencoded using the H.264/MPEG-4 AVC (H.264) codec into a H.264 bitstream.A properly-encoded H.264 bitstream contains sufficient information todecode the encoded frames using a decoder. H.264 encoded frames of avideo are typically referred to as pictures; however, for simplicity,this description will use the term “frame” to refer generically to H.264pictures and frames of a video. The H.264 bitstream is divided intopackets known as Network Abstraction Layer (NAL)-packets. Other codecsmay also format data streams into packets, or may use alternate dataformats.

FIG. 4A illustrates an example NAL packet 400. As shown, the NAL packet400 is divided into a header 402 and a payload 406. The header 402 mayindicate the type of the packet. Types of NAL packets may include framedata (e.g. slice data) or header data (e.g. a parameter set), amongothers. Based on the type of the packet, the payload may then containdifferent types of data.

FIG. 4B then illustrates an example H.264 bitstream 420 that includes asequence of NAL-packets of different types. Bitstream 420 includes tworepresentative slice data packets 428 and 430, and may includeadditional slice data packets, as shown. Frames of a H.264 bitstream aredivided into one or more slices, which represent the content of theframe. Although H.264 bitstreams may divide frames into two or moreslices, H.264 bitstreams may also represent all of the content of eachframe as one respective slice.

Bitstream 420 includes two types of headers: a Sequence Parameter Set(SPS) 422 and a Picture Parameter Set (PPS) 424. The Sequence ParameterSet 422 contains information referring to a sequence of NAL packets(e.g. a sequence of slice packets representing frames of a video). TheSPS 422 may indicate various information about a sequence, such as theheight and width of frames represented by the sequence. The PictureParameter Set (PPS) 424 contains information referring to one or moreframes.

Bitstream 420 also includes instantaneous decoding refresh (IDR) packet426. A IDR packet contains the information necessary to decode oneframe. Some H.264 bitstreams use predictive encoding, which involvesreferencing information in other packets to encode or decode frames. Adecoder may decode one or more subsequent frames in the bitstream byreference to the IDR packet. IDR packets may also be referred to askey-frames or I-frames.

Referring back to the representative slice data packets 428 and 430,each slice data packet, like other NAL packets, may include a sliceheader and data. Slice data packet 428 is shown by way of example asincluding a slice header 440 and data 442. Data 442 is further dividedinto a macroblock array 460. The macroblock array 460 includes at leastone macroblock 462, but may include a plurality of macroblocks, asshown. The H.264 format divides slices into processing units known asmacroblocks. Many video codecs use some type of processing unit. Theterm macroblock is used in this description to refer to H.264macroblocks, as well as macroblocks in other MPEG codecs, coding treeunits in the H.265 codec, megablocks in the VP8/9 codecs, and any othersimilar or equivalent part of a frame in any codec.

In the H.264 codec, the slice header contains information about theslice. For instance, the slice header may indicate the address of thefirst macroblock in the slice, among other parameters. Under H.264,macroblocks in a frame are addressed in raster scan order (i.e.left-to-right, top-to-bottom). Other codecs may address component partsof frames in different ways, all of which are contemplated herein. Theslice header may also indicate which slice of a frame that the packetbelongs to, such as the first slice or the second slice.

FIG. 5A illustrates example frames 502 a and 504 a, which are exampleframes of the first video and the second video, respectively. All of thecontent of frames 502 a and 504 a are represented as one slice. FIG. 5Billustrates example slices 502 b and 504, which represent example frames502 a and 504 a, respectively. Example slices 502 b and 504 b are eachdivided into 16 macroblocks that are addressed from 0-15 in raster scanorder.

While FIG. 5B shows the macroblocks of slices 502 a and 504 b in rasterscan order, in the bitstream, the macroblocks of each slice may besequential elements of a macroblock array, as exemplified by array 460of FIG. 4B. By referencing data in the header, such as the height andwidth of the slice and the address of the first macroblock in the slice,a decoder can arrange a sequence of macroblocks into a frame. Forinstance, slice 502 b has a height of 4 macro blocks, a width of 4macroblocks, and the first macroblock in the slice is at address 0.Therefore, under raster scan ordering (left-to-right, top-to-bottom),the first macroblock of slice 502 b is at address 0 in the top-leftcorner of the frame, as shown in FIG. 5B. Since the width of the sliceis 4 macroblocks, the first row includes the first four macroblocks ofthe frame, addressed at macroblock 1, 2, and 3, respectively, as shown.The second row includes the next four macroblocks, the third rowincludes the next four macroblocks after those, and the fourth rowincludes the last four macroblocks, also as shown. As noted above, theheight of the slice is 4 macroblocks, and, accordingly, there are fourrows of macroblocks in the array.

While a H.264 bitstream is described by way of example, this disclosurecontemplates the different formats used by other codecs. Terms usedthroughout the description in describing components of H.264 areintended to refer to the H.264 component as well as any equivalentstructures in other codecs. For instance, “header” refers to H.264headers such as the Sequence Parameter Set, the Picture Parameter Set,and each slice header. And, “header” also refers generically to anyportion of a data stream that contains information about the datastream. “Frame” refers to H.264 pictures or frames, and also refersgenerically to corresponding structures in any other codec. “Macroblock”refers specifically to H.264 and generically to sub-components of aframe as used by other codecs. Other terms used within the specificationare intended to refer generally to other codecs, as well.

At block 304, the method 300 involves combining the received first datastream and the received second data stream into an output data stream.The output data stream may represent encoded frames of the first videoand encoded frames of the second video such that a decoder may decodethe output data stream into an output format that represents both thefirst video and the second video.

The output data stream may be configured to represent encoded outputframes. The processor may combine a frame from the first data stream anda frame from the second data stream into an encoded output frame. FIG.5C illustrates an example output frame 500 that includes a first slice502 c and a second slice 504 c. The processor may combine a frame fromthe first data stream (e.g. frame 502 a which is represented by slice502 b) and a frame from the second data stream (e.g. frame 504 a whichis represented by slice 504 b) into encoded output frame 500.

The processor may combine frames from the received data streams intodifferent arrangements. In some embodiments, the processor may arrangethe frames from the received data streams into a vertical stack. Forexample, slice 502 c of FIG. 5C is vertically stacked onto slice 504 c.In other embodiments, the processor may arrange the frames from thereceived data streams into a grid.

For decoding by particular decoders, the processor may configure theframes of the received data streams into different arrangements. Forinstance, some decoders may support decoding frames that are no widerthan a maximum frame width. Further, the maximum frame width supportedby some decoders may be relatively narrow, such that some horizontalarrangements of frames may exceed the maximum frame width. To arrangeframes from the received data streams for such decoders, the frames maybe vertically stacked upon one another, creating a relatively tall andnarrow frame. FIG. 6 illustrates an example frame 600 that includesslices 602, 604, 606, and 608 in a vertically stacked configuration.Further, some decoders may support decoding frames up to relativelynarrow maximum frame height, which may be exceeded when a certain numberof frames are vertically stacked. In such a circumstance, the processormay arrange the frames into a grid. FIG. 7 illustrates an example frame700 in which slices 702, 704, 706, and 708 are arranged into arectangular grid.

The processor may combine frames from the first data stream and thesecond data stream on a frame-by-frame basis. As noted above, the firstvideo and the second video may be represented by first frames insequence and by second frames in sequence, respectively. Each sequenceof frames may include a first frame, a second frame, a third frame, andso on. The processor may combine the first frame of the first datastream and the first frame of the second data stream into the firstoutput frame of the output data stream. The processor may also combinethe second frame of the first data stream and the second frame of thesecond data stream into the second output frame of the output datastream. The processor may repeat this process until it reaches the lastframe of either data stream.

FIG. 8 illustrates an example data stream 802 (i.e. a first data stream)and an example data stream 804 (i.e. a second data stream). Data stream802 represents a sequence of eight frames of a first video. Each frameof the sequence is marked with its position in the sequence from 0 to 7,as shown. Similarly, data stream 804 represents a sequence of eightframes of a second video and each frame of the sequence is marked withits position in the sequence from 0 to 7, as shown. Data stream 806(i.e. an output data stream) represents the combination of data stream802 and data stream 804. Like data stream 802 and 804, data stream 806represents a sequence of eight frames of a video and each frame of thesequence is marked with its position in the sequence from 0 to 7. Aprocessor has combined data streams 802 and 804 into data stream 806.The frame of data stream 806 at position 0 represents the frame of datastream 802 at position 0 and the frame of data stream 804 at position 0.Similarly, the frame of data stream 806 at position 1 represents theframe of data stream 802 at position 1 and the frame of data stream 804at position 1. And, the frames of data stream 806 at positions 2-7represent the frames of data stream 802 at position 2-7 and the framesof data stream 804 at position 2-7, respectively.

The processor may combine the first data stream and the second datastream into the output data stream using a variety of techniques. Forexample, the processor may decode the data streams, combine the videointo an output video, and then encode the output video into the outputdata stream. Alternatively, the processor may combine the first datastream and the second data stream into the output data stream withoutfully decoding the first data stream and the second data stream. Forinstance, the processor may generate the output stream and arrange theencoded frames within the output stream. Alternatively, the processormay modify the first data stream to include the second data stream.Other examples are possible as well.

As noted above, in some embodiments, a decoder may decode the first datastream and the second data stream before the processor combines framesof the first data stream with frames of the second data stream. Forexample, an application executing on a mobile computing device, such asa smartphone or tablet computer, may request the first video and thesecond video from a server that is accessible over a network, such asthe Internet. The server may then send the first video and the secondvideo, as a first data stream and a second data stream, respectively, toan intermediate computing device (e.g. a server) having one or morevideo encoder/decoders and at least one processor. The one or more oneor more video encoder/decoders may decode the first data stream and thesecond data stream into the first and second video. The processor of theintermediate computing device may then combine the frames of the firstvideo with frames of the second video into an output video. The one ormore one or more video encoder/decoders may then encode the output videointo the output data stream. The intermediate computing device may thensend the output data stream to the mobile computing device, which maydecode the output data stream using its decoder.

In some embodiments, combining the received data streams into an outputdata stream may involve defining in one or more headers of each receiveddata stream that the frames represented by the received data stream arecomponent parts of the output data stream. For instance, referring backto FIGS. 5A-C, frame 502 a of the first video may be represented byslice 502 b of the first data stream. Within the first data stream,slice 502 b may be a particular NAL packet of the slice data type. Theslice data packet may have a header containing one or more parametersthat indicate to a decoder that slice 502 b (and in turn, frame 502 a)is part of the first data stream. Slice 504 b may also have its ownheader indicating that slice 504 b (and thus frame 504 a) is part of thesecond data stream. When a decoder decodes a slice data packet, thedecoder may reference the one or more parameters in determining whichdata stream the slice data packet is in. NAL packets of the same datastream may each have the same indication within their respective header,which may group the packets into the same video when decoded.

The processor may use such parameters to combine the first data streamand the second data stream into the output data stream. For each frameof the received first data stream, the processor may decode (or parse)from a header of the first data stream, one or more parameters thatindicate that the frame is a slice of the first data stream. Then, theprocessor may define (or re-define) the one or more parameters toindicate that the frame is a first slice of a respective output frame.And, for each frame of the received second data stream, the processormay decode one or more parameters, from a header of the second datastream, that indicate that the frame is a second slice of the respectiveoutput frame. For instance, the processor may define in a header ofslice 502 b that slice 502 b is slice 502 c of frame 500 and also definein a header of slice 504 b that slice 504 b is slice 504 c of frame 500.Then, for example, when frame 500 is decoded, the decoder will arrangethe content of frame 502 a as slice 502 c of frame 500 of the outputdata stream, rather than as slice 502 b of the first data stream. Andthe decoder will arranged the content of frame 504 a as slice 504 c offrame 500 of the output data stream.

The specific parameters in the header used to indicate that the frame isa slice of an output frame may vary based on the codec used to encodethe received data streams. In some cases, one or more parameters mayexplicitly define the frame as a slice of an output frame. In othercases, the one or more parameters may implicitly define the frame as aslice of an output frame. For instance, changing an address in a headermay define the frame as a slice of an output frame.

To generate the output data stream, the processor may create a headerdefining the output data stream. For instance, with H.264, the processormay create a SPS packet. The header of the output data stream mayindicate that the output frames are part of the output data stream. Theprocessor may also define various parameters of the output data streamin the header, such as the output frame height and the output framewidth. Some of the parameters may be based on aspects of the first datastream and/or the second data stream. For instance, the processor maydecode (or parse) from the first data stream and the second data stream,a first frame height and a second frame height, which may indicate theheight of frames of the first data stream and the second data stream,respectively. Then, when vertically stacking frames, the processor maydefine in the header the height of the output frames as the sum of thefirst frame height and the second frame height. For instance, whencombining slice 502 b and 504 b into frame 500, the processor may definethe frame height of the output data stream as 8 macroblocks and theframe width as 4 macroblocks, as the two slices are each 4 macroblockshigh and 4 macroblocks wide.

Alternatively, to generate the output data stream, the processor maydefine the first data stream as the output stream and then concatenateframes from the other received data streams to the first data stream.The processor may also decode parameters from one or more headers of thefirst data stream and re-define the one or more parameters as necessary.For instance, the processor may parse out the frame height of the firstdata stream and re-define the frame height as the sum of the frameheights of the frames of the first data stream and the heights of theframes of each additional data stream that is combined with the firstdata stream.

To arrange a frame of the first data stream and a frame of the seconddata stream within the output frame, the processor may define (orre-define) various parameters contained within one or more headers ofthe received data streams or in a header of the output data stream. Asnoted above, slice headers may contain an indication of the address ofthe first macroblock in the slice. For instance, when combining slice502 b and 504 b into frame 500 (i.e. a vertically stackedconfiguration), the processor may define the address of the firstmacroblock of slice 504 c as address 16. Address 16 is incremented, by amacroblock, from the address of the last macroblock of the first slice(i.e. address 15, indicating the sixteenth macroblock of slice 502 c).As another example, referring to FIG. 6, to arrange slices 602, 604,606, and 608 into a vertically stacked configuration as shown, theprocessor may define the address of the first macroblock of the firstslice (slice 602) as 0. The processor may also define addresses of thefirst macroblock of slices 604, 606, and 608 as 16, 32, and 48,respectively. Each of these addresses is incremented by one macroblockfrom the address of the last macroblock of the preceding slice. Bydefining the position of the first macroblock in the slice for slices604, 606, and 608 in this way, the processor may vertically concatenateeach macroblock array of each slice to the preceding array.

The processor may also use such techniques in combining a respectiveframe of each received data stream into an output frame having a gridlayout. Consider, for example, that the processor receives a first datastream, a second data stream, a third data stream, and a fourth datastream. Each received data stream represents frames of a respectivevideo. Frames of each video are represented in the data stream as onefour by four slice that is divided into an array of sixteen macroblocks.By way of example, slices 702, 704, 706, and 708 of FIG. 7 may representsuch slices. To arrange slices 702, 704, 706, and 708 into therectangular grid arrangement of FIG. 7, the processor may define theaddresses of the first macroblock of slices 702, 704, 706, and 708 asaddress 0, address 4, address 32, and address 36. In this manner, thearray of macroblocks in slice 704 is horizontally-concatenated to thearray of macroblocks in slice 702. And, the array of macroblocks inslice 706 is vertically concatenated to the array of macroblocks inslice 702, and the array of macroblocks in slice 708 is horizontallyconcatenated to the array of macroblocks in slice 706.

As noted above, some decoders may have maximum frame height and/ormaximum frame width limitations. In some cases, the processor may use agrid layout to avoid these limitations. For instance, the processor mayarrange two frames into a vertically stacked configuration if the sum ofthe respective frame heights of each of the two frames is less than orequal to a maximum frame height of a particular decoder. And, if the sumof the respective frame heights of each of the two frames is greaterthan a maximum frame height of a particular decoder, the processor mayarrange the two frames horizontally. Such a configuration may indicate apreference for a vertically stacked configuration of frames. Someembodiments may prefer a different configuration of frames.

Some codecs require sequencing of the component parts of a frame (e.g.slices and macroblocks) in decoding order (e.g. raster scan order).However, some combinations of frames of received data streams intooutput frames may result in the array of macroblocks of each slicereaching the decoder out of decoding order. The processor and thedecoder may then decode the slices out of order. For instance, H.264includes a feature called arbitrary slice ordering that allows thedecoder to receive slices of an output frame in any order. For eachslice, the processor may decode one or more parameters indicating theslice length of the slice (i.e. the number of elements in the macroblockarray) and the macroblock address of the first macroblock in the slice.The processor may then use the one or more decoded parameters to sendeach slice individually to the decoder. The decoder may then decode theframe after it has received all of the slices of the frame, or thedecoder may decode the slices in the order in which they come to thedecoder.

Some decoders may require that the encoded frames of the output datastream have a consistent frame width. Within examples, the processor maydecode from a header of the first data stream a first frame width thatindicates the width of the encoded frames of the first data stream. Theprocessor may also decode from a header of the second data stream asecond frame width that indicates the width of the encoded frames of thesecond data stream. The processor may then determine that the firstframe width is equivalent to the second frame width. Then, at somepoint, such as during generation of the output data stream, theprocessor may define in a header of the output data stream that theencoded output frames have a width that is equal to the encoded frames.

However, in some cases, the encoded frames of the first data stream andthe encoded frames of the second data stream may have different framewidths. In some examples, the method may then further involve paddingthe frames of one of the received data streams to make the frames widthsequal. For instance, referring to FIG. 9, slices 902 a and 904 a mayrepresent a frame of a first data stream and a frame of a second datastream, respectively. Slice 902 a and 904 a have frame widths of 4macroblocks and 3 macroblocks, respectively. The processor may determinethat the frame width of slice 904 a is less than the frame width ofslice 902 a. The processor may then pad the slice 904 a with additionalmacroblock data such that the width of slice 904 a is equal to the widthof slice 902 b. The processor may then combine slice 902 a and slice 904a into output frame 900. After output frame 900 is decoded, theprocessor may provide for display the frame of the second data streamwithout the additional macroblock data.

In some cases, the first video (represented by the first data stream)and the second video (represented by the second data stream) may havedifferent frame rates. For example, referring to FIG. 10, data stream1002 may represent a first video having a first frame rate that is threetimes the second frame rate of a second video that is represented bydata stream 1004. Within examples, the processor may insert frames intothe second data stream so that the frame rates of the data streams areequivalent. For instance, the processor may insert two frames into datastream 1004 after every frame of the second data stream. Then datastream 1002 and data stream 1004 are combined into data stream 1006 withthe same frame rate. So that the content of the second video is notaltered, the content of each inserted frame may represent content of aframe that neighbors the inserted frame with the second data stream. Forinstance, a type of frame known as a P-frame which consists of P_SKIPmacroblocks may be inserted into the frames such that the content of theinserted frame represents the content of the preceding frame. P-framesuse data from previous frames to decode the content in the P-frame.

Further, some codecs may require the key-frame intervals of receiveddata streams to be equivalent in order to decode the output data streamwhen the received data streams are combined. Key-frames (also known asI-frames) do not require other video frames to decode. The processor mayinsert frames to make the key-frame intervals of the received datastreams equivalent. For instance, when the second video has a lowerframe rate than the first video, the processor may insert, after eachkey-frame in the second data stream, a particular number of frames. Insome examples, the inserted frames may be P-frames which consist ofP_SKIP macroblocks. As noted above, the particular number of frames maybe proportional to the difference in the frames rates of the receiveddata streams.

Other codecs may permit different key-frame intervals. With such codecs,the processor may combine different types of frame types for decoding bya decoder compatible with the codec. For instance, the processor maycombine a I-frame from the first data stream with a P-frame from thesecond data stream.

At block 306, the method involves decoding the output data stream intoan output surface format that includes, in respective non-overlappingregions, decoded frames of the first video and decoded frames of thesecond video. For instance, processor 212 of FIG. 2 may decode theoutput data stream using a decoder 222 that is a component of processor212. Alternatively, processor 212 may provide output data stream to adifferent processor, such as GPU 214, which may decode the output datastream using decoder 224. As another example, processor 212 may send theoutput data stream to a decoder on another computing device, such as amobile computing device, via interface 202.

The output surface format may, for example, represent each frame of theoutput data stream as an array of pixel data. Each array of pixel datamay represent a frame of the first video and a frame of the second videoin a different region. The processor may then sample from the differentregions to divide the output surface format into the first video and thesecond video.

At block 308, the method involves providing the decoded frames of thefirst video and the decoded frames of the second video display. Forinstance, processor 212 may provide the decoded frames to interface 202.As noted above, interface 202 may include a screen, such as atouchscreen, which may display the decoded frames of each video whenthey are provided to interface 202 by the processor.

In some examples, the processor 212 may provide the first video and thesecond video for display at different times. For instance, at a firstpresentation time, the processor 212 may sample the first video from theoutput surface format and provide the first video for display. At asecond presentation time, the processor 212 may sample the second videofrom the output surface format and provide the second video for display.

In other examples, processor 212 may provide the first video and thesecond video for concurrent display. Concurrent display of the firstvideo and the second video may involve positioning the decoded frames ofeach video in respective arbitrarily-located positions on a display.Concurrent display of the first video and the second video may havevarious applications. As one example, the first video (represented inthe first data stream) and the second video (represented in the seconddata stream) may represent a video call from a first device and a videocall from a second device respectively. By combining the video callsfrom the two devices and decoding the video calls as a combined outputdata stream, both video calls may be hardware-decoded simultaneously,which may enable assorted features of a video chat application. Forexample, the video chat application may support a greater number ofconcurrent users in a single group chat or display video calls during agroup chat at higher frame rates.

In some examples, the first video and the second video may representvideo previews of respective videos. For instance, a news feedapplication may provide for display of a video preview next to each newsitem. By application of the present method, the processor may combinethe video previews into an output data stream and then decode themtogether by decoding the output data stream. This may enable variousfeatures of the news feed application. For instance, two or more of thevideo previews may play concurrently. Alternatively, a video galleryapplication may indicate each video in the gallery using a videopreview. Other applications are possible as well.

Within examples, the processor may divide received data streams intosets. The processor may then combine the data streams in the set into anoutput data stream. The processor may select particular data streams foreach group based on characteristics of the data stream. For instance, asnoted above, some decoders may require that the key-frame intervals ofthe combined data streams are equivalent. From received data streams,the processor may parse one or more parameters that indicate thekey-frame interval of the data stream. Then the processor may select, asa set, particular data streams having the same key-frame interval.Similarly, the processor may select particular data streams havingframes of the same frame width as a set. Selection based on otherparameters, such as frame rate, is possible as well.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims, along with the full scope ofequivalents to which such claims are entitled. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

What is claimed is:
 1. A method comprising: receiving a first datastream that represent a first video, wherein the first data streamincludes a first sequence of frames that includes first intra-codedframes; receiving a second data stream that represent a second video,wherein the second data stream includes a second sequence of frames thatincludes second intra-coded frames; and combining the received firstdata stream and the received second data stream to obtain an output datastream of encoded output frames such that an encoded output frameincludes a respective frame of the first sequence and a respective frameof the second sequence and that first intra-coded frames are combinedwith respective second intra-coded frames in respective encoded outputframes within the output stream.
 2. The method of claim 1, whereincombining the received first data stream and the received second datastream into an output data stream of encoded output frames furthercomprises: combining first inter-coded frames of the first data streamwith respective second inter-coded frames of the second data stream. 3.The method of claim 1, wherein the first encoded frames are divided intoa respective first coding unit arrays, and wherein the second encodedframes are divided into respective second coding unit arrays, andwherein combining the received first data stream and the received seconddata stream comprises combining a given first coding unit array with agiven second coding unit array to obtain an encoded output frame.
 4. Themethod of claim 1, further comprising: determining that the frames ofthe first sequence of frames have a first frame width and that theframes of the second sequence of frames have a second frame width thatis less than the first frame width; and padding the frames of the secondsequence of frames with additional frame data such that the frames ofthe first sequence of frames and the frames of the second sequence offrames have the same frame width.
 5. The method of claim 1, wherein thefirst video has a first frame rate that is higher than a second framerate of the second video, the method further comprising: after secondintra-coded frames of the second data stream, inserting a particularnumber of frames into the second data stream, wherein the particularnumber of frames is proportional to a difference between the first framerate and the second frame rate.
 6. The method of claim 1, furthercomprising: decoding, by a decoder, the output data stream of encodedoutput frames into an output surface format that includes decoded framesof the first video and decoded frames of the second video.
 7. The methodof claim 1, wherein each of the first data stream and the second datastream represents one of: a video preview, a video advertisement, or avideo call.
 8. A non-transitory computer readable medium having storedtherein instructions, that when executed by a processor, cause theprocessor to perform operations, the operations comprising: receiving afirst data stream that represent a first video, wherein the first datastream includes a first sequence of frames that includes firstintra-coded frames; receiving a second data stream that represent asecond video, wherein the second data stream includes a second sequenceof frames that includes second intra-coded frames; and combining thereceived first data stream and the received second data stream to obtainan output data stream of encoded output frames such that an encodedoutput frame includes a respective frame of the first sequence and arespective frame of the second sequence and that first intra-codedframes are combined with respective second intra-coded frames inrespective encoded output frames within the output stream.
 9. Thecomputer readable medium of claim 8, wherein combining the receivedfirst data stream and the received second data stream into an outputdata stream of encoded output frames further comprises: combining firstinter-coded frames of the first data stream with respective secondinter-coded frames of the second data stream.
 10. The computer readablemedium of claim 8, wherein the first encoded frames are divided into arespective first coding unit arrays, and wherein the second encodedframes are divided into respective second coding unit arrays, andwherein combining the received first data stream and the received seconddata stream comprises combining a given first coding unit array with agiven second coding unit array to obtain an encoded output frame. 11.The computer readable medium of claim 8, wherein the operations furthercomprise: determining that the frames of the first sequence of frameshave a first frame width and that the frames of the second sequence offrames have a second frame width that is less than the first framewidth; and padding the frames of the second sequence of frames withadditional frame data to obtain padded frames having the first framewidth.
 12. The computer readable medium of claim 8, wherein the firstvideo has a first frame rate that is higher than a second frame rate ofthe second video, the method further comprising: after secondintra-coded frames of the second data stream, inserting a particularnumber of frames into the second data stream, wherein the particularnumber of frames is proportional to a difference between the first framerate and the second frame rate.
 13. The computer readable medium ofclaim 8, wherein the operations further comprise: decoding, by adecoder, the output data stream of encoded output frames into an outputsurface format that includes decoded frames of the first video anddecoded frames of the second video.
 14. The computer readable medium ofclaim 8, wherein each of the first data stream and the second datastream represents one of: a video preview, a video advertisement, or avideo call.
 15. A device comprising: one or more processors; and datastorage configured to store instructions, that when executed by the oneor more processors, cause the device to: receive a first data streamthat includes a sequence of first encoded frames, wherein each firstencoded frame is divided into a respective first coding unit array;receive a second data stream that includes a sequence of second encodedframes, wherein each second encoded frame is divided into a respectivesecond coding unit array; combine the received first data stream and thereceived second data stream into an output data stream of encoded outputframes such that an encoded output frame includes a first coding unitarray and a second coding unit array, wherein intra-coded coding unitarrays of the first sequence are combined with respective intra-codedcoding unit arrays of the second sequence.
 16. The device of claim 15,wherein combining the received first data stream and the received seconddata stream into an output data stream of encoded output frames furthercomprises: combining first inter-coded frames of the first data streamwith respective second inter-coded frames of the second data stream. 17.The device of claim 15, wherein the instructions further cause thedevice to: determine that the frames of the first sequence of frameshave a first frame width and that the frames of the second sequence offrames have a second frame width that is less than the first framewidth; and pad the frames of the second sequence of frames withadditional coding unit data to obtain padded frames having the firstframe width.
 18. The device of claim 15, wherein the first data streamrepresents a first video having a first frame rate, and wherein thesecond data stream represents a second video having a second frame ratethat is low than the first frame rate, the method further comprising:after second intra-coded frames of the second data stream, inserting aparticular number of frames into the second data stream, wherein theparticular number of frames is proportional to a difference between thefirst frame rate and the second frame rate.
 19. The device of claim 15,wherein the instructions further cause the device to: decoding, by adecoder, the output data stream of encoded output frames into an outputsurface format that includes decoded frames of the first video anddecoded frames of the second video.
 20. The device of claim 15, whereincombining the received first data stream and the received second datastream comprises concatenating a given first coding unit array with agiven second coding unit array to obtain an encoded output frame.